Hydroalumination of bis(alkynyl)germanes and -silanes: Generation of a chelating Lewis-acid and observation of a dismutation reaction

Article abstract of DOI:10.1016/j.ica.2011.02.070

Treatment of diphenyl-di(phenylethynyl)germane with two equivalents of di(tert-butyl)aluminum hydride afforded the corresponding dialkenyl derivative, Ph₂Ge[C(AltBu₂)C(H)-Ph]₂ (1) by dual hydroalumination. The aluminum ato

Full text of DOI:10.1016/j.ica.2011.02.070

Inorganica Chimica Acta 374 (2011) 359–365
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Hydroalumination of bis(alkynyl)germanes and -silanes: Generation
of a chelating Lewis-acid and observation of a dismutation reaction
⇑
Werner Uhl , Denis Heller, Martina Rohling, Jutta Kösters
Institut für Anorganische und Analytische Chemie der Universität Münster, Corrensstraße 30, 48149 Münster, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 3 March 2011
Treatment of diphenyl-di(phenylethynyl)germane with two equivalents of di(tert-butyl)aluminum
hydride afforded the corresponding dialkenyl derivative, Ph2Ge[C(AltBu2)@C(H)–Ph]2 (1) by dual hydroa-
lumination. The aluminum atoms of 1 are attached to the carbon atoms in a-position to germanium. They
Dedicated to Prof. W. Kaim on the occasion
of his 60th birthday.
are coordinatively unsaturated and are able to act as chelating Lewis-acids and to coordinate donors such
as chloride or bromide anions in a chelating manner (2, 3). The analogous reaction of the corresponding
silicon-centered dialkyne with two equivalents of dimethylaluminum hydride gave a mixture of
unknown compounds. Interestingly, equimolar quantities of the hydride and the dialkyne resulted in dis-
mutation and the formation of the unprecedented compound MeAl[C(@CH–Ph)–SiPh2–C„C–Ph]2 (4).
Compound 4 has two alkenyl groups bonded to the central aluminum atom and a terminal alkynyl group
attached to each silicon atom. An attempt to reduce the remaining triple bonds by reaction with di(tert-
butyl)aluminum hydride resulted in cleavage and isolation of the monoalkenyl compound tBu2Al–
C[@C(H)–Ph]–SiPh2–C„C–Ph (5). The molecular structure of 5 showed a close interaction between the
Keywords:
Aluminum
Hydroalumination
Silicon
Germanium
Chelating Lewis-acid
Condensation
a-carbon atom of the triple bond and the coordinatively unsaturated aluminum atom.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Lewis-acids was impressively shown by the generation of carbo-
cationic species which were formed via C–H bond activation and
the chelating coordination of the released hydride anion by two
aluminum atoms [6]. The dual hydroalumination or hydrogallation
of dialkynylsilanes or -germanes may allow an alternative access to
chelating Lewis-acids that have longer chains between the alumi-
num or gallium acceptor atoms.
Oligoacceptors based on coordinatively unsaturated atoms of
main-group elements (chelating Lewis-acids) are of interest in
phase transfer processes, in catalysis or in molecular recognition.
The synthesis of such compounds and their application for the
coordination of suitable donors has found considerable interest
in recent research [1]. Previously our group has synthesized a
methylene bridged dialuminum compound, R2Al–CH2–AlR2
[R = CH(SiMe3)2] [2], which features two coordinatively unsatu-
rated aluminum atoms as particularly effective Lewis-acids and
was able to coordinate various donors such as hydride, nitrate,
azide or acetate anions in a chelating manner [3]. Although this
compound proved to be an excellent chelating acceptor, its appli-
cation is relatively limited due to the low variability of the distance
between the coordinating aluminum atoms and the presence of
only two coordinatively unsaturated atoms in a molecule. In order
to overcome these problems and to achieve a higher flexibility we
have used the hydroalumination and hydrogallation of oligoalky-
nes for the generation of organoelement compounds with up to
four tricoordinated metal atoms [4]. Preliminary experiments have
confirmed their applicability for the coordination of halide, benzo-
ate or thiophenolate anions [5]. The efficacy of these chelating
2. Results and discussion
2.1. Reactions of dialkynylgermanes
Only recently we have published the reactions of dimethyl- and
diphenyl-(diphenylethynyl)germanes with equimolar quantities of
various dialkylaluminum hydrides [7]. One C„C triple bond of
each starting compound was reduced, and mixed alkenyl–alkynyl-
germanium compounds have been isolated in 55–90% yield. The
hydrogen and aluminum atoms of the resulting alkenyl groups
were in all cases cis to each other. The thermodynamically favored
cis/trans-isomerisation [8] is prevented by an interaction of the
coordinatively unsaturated aluminum atoms with the
a-carbon
atoms of the ethynyl groups which carry a relative high negative
partial charge. Only the sterically shielded bis(trimethylsilyl)meth-
ylaluminum derivatives did not show this interaction [7]. Hydroa-
lumination of both alkynyl groups of the dialkynylgermanium
⇑
Corresponding author. Fax: +49 251 8336660.
E-mail address: uhlw@uni-muenster.de (W. Uhl).
starting compounds was successful only in a single case
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.070

360
W. Uhl et al. / Inorganica Chimica Acta 374 (2011) 359–365
(Scheme 1). Treatment of (H5C6)2Ge(C„C–C6H5)2 with two equiv-
alents of di(tert-butyl)aluminum hydride in n-hexane afforded the
colorless dialkenylgermanium compound 1 in 53% yield after a rel-
atively long reaction time of 7 d at room temperature. Heating of
the reaction mixture in order to increase the reaction rate did
not result in a faster reaction, but decomposition occurred with
the formation of several unknown products. Other dialkylalumi-
num hydrides such as Me2AlH, (Me3CCH2)2AlH or (Me2CHCH2)2AlH
led to the elimination of the corresponding dialkylaluminum alky-
nides, R2Al–C„C–C6H5 [9], which were identified by NMR spec-
troscopy and in two cases by determination of unit cell
parameters. We were not able to isolate any secondary product
containing the germanium atoms. Several resonances in the NMR
spectra of the highly viscous residues may indicate an unselective
decomposition. Hence, it is not possible to discuss a rational reac-
tion course for these interesting elimination processes. Similar
degradation reactions were observed in the case of dimethyl-
di(phenylethynyl)germanium. In contrast, a broader variety of
dialkenyl species could be isolated with analogous silicon-centered
dialkynes [10].
NMR data confirm the molecular structure of 1 which is sche-
matically given in Scheme 1. The 13C NMR spectrum shows only
the characteristic resonances of alkenyl groups (d = 157.4 and
163.3), signals of ethynyl moieties are missing. The resonance of
the vinylic hydrogen atoms is shifted towards the low field side
of the 1H NMR spectrum (d = 8.35) which is in accordance with pre-
viously obtained results [4,10]. A crystal structure determination
(Fig. 1) revealed a central germanium atom which is bonded to
two phenyl and two alkenyl groups in a slightly distorted tetrahe-
dral arrangement. The bond angles C–Ge–C are in a narrow range
between 106.4(1)° and 110.78(9)° with the largest one between
the alkenyl carbon atoms. The tricoordinated aluminum atoms re-
side 12 pm above the plane formed by the three adjacent carbon
atoms. Steric repulsion in this relatively crowded molecule may
cause the deviation from planarity; any secondary intramolecular
interaction was not observed. The dialkylaluminum groups occupy
the a-positions of the alkenyl groups neighboring the germanium
atoms. The reaction of the positively charged aluminum atoms at
these positions is favored by the relatively high negative charge
of these alkynyl carbon atoms [11]. In contrast to the mixed alke-
nyl–alkynyl species discussed above trans-configuration results for
both alkenyl groups with aluminum and hydrogen atoms on differ-
ent sides of the C@C double bonds (C@C bond lengths
134.7(2) pm). cis/trans-Rearrangement to yield the thermodynam-
ically favored isomer [8] is not hindered by an intramolecular
interaction as described above. Further distances and angles are
in the expected ranges and do not require a detailed discussion.
The molecular conformation is determined by a minimization of
steric repulsion between the bulky di(tert-butyl)aluminum groups
which arrange themselves as far apart as possible.
Compound 1 has two coordinatively unsaturated aluminum
atoms and should behave as a chelating Lewis-acid. In order to
check this property in some preliminary experiments we treated
solutions of 1 in toluene with equimolar quantities of tetra
(n-butyl)ammonium chloride and bromide (Scheme 1). Colorless
solids precipitated in both cases and were isolated by filtration.
The residues consist of the analytically pure adducts 2 and 3 with-
out further purification. With the exception of the resonances of
Fig. 1. Molecular structure and numbering scheme of 1; the thermal ellipsoids are
drawn at the 40% probability level; hydrogen atoms with the exception of the
vinylic hydrogen atom are omitted. Selected bond lengths [pm] and angles [°]: Ge1–
C11 194.9(2), Ge1–C21 195.6(2), C11–C12 134.7(2), Al1–C11 197.1(2), Al1–C31
198.6(2), Al1–C41 199.2(2), C11–Ge1–C11’ 110.78(9), C21–Ge1–C210 106.4(1),
Ge1–C11–Al1 127.05(8), Al1–C11–C12 115.0(1); C110 and C210 generated by
ꢀx + 0.5, ꢀy + 0.5, z.
Scheme 1.

W. Uhl et al. / Inorganica Chimica Acta 374 (2011) 359–365
361
the n-butyl groups the NMR parameters are almost identical to
those of the starting compound 1. Only the resonances of the
vinylic protons are shifted considerably to a higher field in the
1H NMR spectrum (d = 7.64 on average versus 8.35 of 1). Crystal
structure determinations verified the coordination of the halide
anions in a chelating manner by both aluminum atoms of 1 (Figs. 2
and 3). The formation of the complexes caused a dramatic change
in the conformation of the germanium compound, because the alu-
minum atoms must approach to facilitate the twofold donor–
acceptor interaction. The Al–Cl (234.8 pm) [12] and Al–Br distances
(254.6 pm) [13] are in the characteristic range for Al–X bond
lengths in Al–X–Al bridges. Due to the larger radius of the bromine
atom the Al–X–Al angle (137.81(6)° versus 126.7° on average) is
smaller for the complex with the heavier halogen atom. All other
angles are almost indistinguishable, e.g. C–Ge–C in the resulting
GeC2Al2X heterocycle 126.9° (on average for 3) versus 125.8(2)°
(2). The shape of the six-membered heterocycles approaches a
half-boat (2; Ge1 44 pm, Cl1 11 pm above the plane Al1, Al2, C1,
C2) or a twist boat conformation (3). The crystals of compound 3
enclose 1,2-difluorobenzene molecules. The shortest intermolecu-
lar Hꢁ ꢁ ꢁF distances are in the range of 255–296 pm which is close
to the sum of the van der Waals radii (>270 pm) and indicates only
weak intermolecular interactions.
Fig. 3. Molecular structure and numbering scheme of 3; hydrogen atoms with the
exception of the vinylic hydrogen atoms and methyl groups of the tert-butyl
substituents (at Al1 and Al2) are omitted. Selected bond lengths [pm] and angles [°]
(values of the second molecule in square brackets): Ge1–C11 198.4(3) [197.6(3)],
Ge1–C12 198.1(3) [197.2(3)], C11–C111 135.1(5) [134.5(5)], C12–C121 133.9(5)
[134.1(5)], Al1–C11 201.4(4) [200.3(4)], Al2–C12 200.5(4) [201.1(4)], Al1–Br1
256.7(1) [253.4(1)], Al2–Br1 254.0(1) [254.3(1)], C11–Ge1–C12 127.7(1)
[126.1(1)], Ge1–C11–Al1 123.6(2) [126.0(2)], Ge1–C12–Al2 124.6(3) [125.1(2)],
C11–Al1–Br1 97.5(1) [98.1(1)], C12–Al2–Br1 96.6(1) [97.2(1)], Al1–Br1–Al2
126.94(4) [126.54(4)].
2.2. Reaction of a dialkynylsilane with dimethylaluminum hydride
A broad variety of compounds analogous to 1 has been synthe-
sized via the dual hydroalumination of dialkynylsilanes [10]. In
contrast, two equivalents of dimethylaluminum hydride gave an
inseparable mixture of many unknown components. Interestingly,
we obtained an unexpected, unprecedented compound when we
repeated this experiment with equimolar quantities of Me2AlH
and (H5C6)2Si(C„C–C6H5)2 (Scheme 2). A dismutation reaction
took place, and we isolated the dialkenyl compound 4 in 71% yield.
Trimethylaluminum was identified by NMR spectroscopy as a by-
product. Compound 4 has a central three-coordinate Al atom
which is bonded to a methyl group and two alkenyl groups. The
latter result from the reduction of one C„C triple bond of the start-
ing dialkyne. Each alkenyl group carries a silicon atom which is
additionally bonded to two phenyl groups and the unaffected, ter-
minal alkynyl substituent. Thus, compound 4 has two alkenyl and
Scheme 2.
Fig. 2. Molecular structure and numbering scheme of 2; the thermal ellipsoids are
drawn at the 40% probability level; hydrogen atoms with the exception of the
vinylic hydrogen atoms and methyl groups of the tert-butyl substituents (at Al1 and
Al2) are omitted. Selected bond lengths [pm] and angles [°]: Ge1–C1 195.8(4), Ge1–
C2 194.9(4), C1–C11 136.7(6), C2–C21 135.6(6), Al1–C1 201.1(4), Al2–C2 203.7(4),
Al1–Cl1 235.4(2), Al2–Cl1 234.1(2), C1–Ge1–C2 125.8(2), Ge1–C1–Al1 126.4(2),
Ge1–C2–Al2 125.0(2), C1–Al1–Cl1 97.7(1), C2–Al2–Cl1 98.4(1), Al1–Cl1–Al2
137.81(6).
two alkynyl groups in a single molecule. A crystal structure deter-
mination (Fig. 4) revealed normal C@C double (134.5 pm on aver-
age) and C„C triple bond lengths (120.1 pm). The Al–C distances
differ slightly with the shortest being observed for the Al–Me

362
W. Uhl et al. / Inorganica Chimica Acta 374 (2011) 359–365
Fig. 4. Molecular structure and numbering scheme of 4; hydrogen atoms are
omitted; only the ipso-C atoms of the phenyl groups (C113, C123, C131, C141, C213,
C223, C231, C241) are shown. Selected bond lengths [pm] and angles [°]: Al1–C1
194.9(3), Al1–C111 197.3(3), Al1–C211 196.2(3), C111–C112 133.9(4), C211–C212
135.1(4), C121–C122 120.0(4), C221–C222 120.1(4), Al1–C111–Si1 121.2(2), Al1–
C211–Si2 123.5(2).
Fig. 5. Molecular structure and numbering scheme of 5; the thermal ellipsoids are
drawn at the 40% probability level; hydrogen atoms with the exception of the
vinylic hydrogen atom are omitted. Selected bond lengths [pm] and angles [°]: Al1–
C11 200.2(2), Al1ꢁ ꢁ ꢁC21 245.8(2), Si1–C11 185.2(2), Si1–C21 187.0(2), C11–C12
133.4(3), C21–C22 120.3(3), C11–Si1–C21 99.61(9), Si1–C21–C22 161.9(2), C21–
C22–C23 176.8(2), Si1–C11–C12 120.9(2), Al1–C11–C12 140.6(2).
group (194.9(3) versus 196.2(3) and 197.3(3) pm). This may be
caused by the different bulk of the substituents. The aluminum
atom has a planar coordination sphere and resides only 0.3 pm
above the plane of the adjacent carbon atoms. The smallest C–
Al–C angle is found between the
a-carbon atoms of the alkenyl
groups (C111 and C211, 116.4(1)°), the angles including the methyl
carbon atom C1 are 121.0(1) and 122.6(1)°. The crystals of 4 incor-
porate 1,2-difluorobenzene molecules. Intermolecular Hꢁ ꢁ ꢁF dis-
tances of >260 pm are in accordance with only weak interactions.
The aluminum and hydrogen atoms of the alkenyl moieties are in
a trans-arrangement on different sides of the C@C double bonds.
cis/trans-Rearrangement, for which intermolecular activation is re-
quired [8], has to be expected in this case due to the relatively low
steric shielding of the aluminum atoms by the methyl group. The
trans-configuration is also evident from the 1H NMR spectrum
pyramidal configuration is caused by an intramolecular interaction
between the coordinatively unsaturated metal atom and the a-car-
bon atom of the ethynyl group with an Al1–C21 distance of
245.8(2) pm. This distance is considerably longer than the normal
values for terminal Al–C bonds (<200 pm), nevertheless several
other observations support the significance of this interaction: (i)
the torsion angle C21–Si1–C11–Al1 is with 8.8° close to the ideal
value of 0° which allows an optimum interaction between alumi-
num and carbon. (ii) The angle C21–Si1–C11 is very small
(99.61(9)°) and indicates considerable steric strain in the resulting
four-membered C2SiAl heterocycle. (iii) The group Si1–C21„C22
deviates from linearity (161.9(2)°; C21„C22–C23 176.8(2)°). (iv)
The angle Al1–C11@C12 is extraordinarily large (140.6°) which is
caused by the close contact between the aluminum atom and the
alkyne carbon atom C21. Similar interactions have been verified
by NMR spectroscopy or crystal structure determinations for vari-
ous products of the hydroboration or hydroalumination of dialky-
nylelement compounds [7,10,15]. Interestingly, 5 is an isomer of a
compound recently published by our group. It was obtained by
hydroalumination of the corresponding dialkynylsilane with
di(tert-butyl)aluminum hydride [10] and had a cis-arrangement
of H and Al atoms at the resulting C@C double bond. cis/trans-
Isomerisation was prevented in this case by an intramolecular
3
and the JSiꢁ ꢁ ꢁH coupling constant (13.5 Hz) which is in the charac-
teristic range of trans-addition products (>20 Hz for cis-configura-
tion). The release of trialkylaluminum or -gallium derivatives and
the formation of divinyl- or trivinylelement compounds has been
reported previously [4,8]. This method was applied for the selec-
tive generation of unprecedented cage compounds and clusters
[14].
Compound 4 possesses two terminal ethynyl groups. Their
reduction via a hydroalumination reaction should afford a com-
pound with three coordinatively unsaturated aluminum atoms in
a single molecule. We therefore treated 4 with two equivalents
of di(tert-butyl)aluminum hydride in toluene at room temperature
(Scheme 2). Colorless crystals of the product 5 were isolated in 71%
yield after recrystallization. Crystal structure determination (Fig. 5)
and spectroscopic characterization of 5 revealed the unexpected
cleavage of the starting compound 4 resulting in the formation of
a mononuclear alkenyl–alkynyl–diphenylsilicon derivative (C@C
133.4(3) pm; C„C 120.3(3) pm). The aluminum atom of 5 is
interaction of the aluminum atom with the
a-carbon atom of the
alkynyl group and, hence, the coordinative saturation of the metal
atom. Rearrangement to the cis-product was not observed even
upon warming. In contrast, the trans-arrangement of hydrogen
and aluminum atoms was found for compound 5, and the thermo-
dynamically favored isomer was formed via the dialkenyl com-
pound 4. The different configurations can easily be derived from
bonded to the
a-carbon atom of the alkenyl group and deviates
from a trigonal planar geometry with the aluminum atom residing
19.2 pm above the plane of the three adjacent carbon atoms. The
3
the JSiꢁ ꢁ ꢁH coupling constants across the C@C double bonds in the

W. Uhl et al. / Inorganica Chimica Acta 374 (2011) 359–365
363
1H NMR spectra which are 13.7 Hz for 5 (trans) and 26.0 Hz (cis) for
the isomeric compound. We were not able to identify any by-prod-
uct of the reaction according to Scheme 2. The compound
‘‘MeAlH2’’ is postulated to balance the equation. Such dihydrides,
RAlH2, bearing small alkyl substituents are unknown in the litera-
ture, only one derivative is reported which has the bulky tri(tert-
butyl)phenyl substituent [16].
In conclusion, hydroalumination of oligoalkynes is a powerful
method for the generation of efficient oligoacceptors (chelating Le-
wis-acids) which are suitable for the coordination of halide anions
and potentially of other anions or donor molecules. However, in
the case of low steric shielding condensation reactions may take
place. They prevent the isolation of chelating Lewis-acids, but lead
to unprecedented secondary products with interesting
functionalities.
were filtered. The residues were evacuated to completely remove
all volatiles.
3.3.1. [Ph2Ge{C(AltBu2)@CHPh}2Cl][N(n–Bu)4] (2)
Yield: 86%. M.p. (sealed capillary, argon): 201 °C. 1H NMR
(400 MHz, C6D6, 300 K): d 7.65 (s, 2H, CHPh), 7.58 (pseudo-d, 4H,
ortho-H GePh2), 7.27 (pseudo-d, 4H, ortho-H CHPh), 7.15 (m, 4H,
meta-H GePh2), 7.13 (m, 4H, meta-H CHPh), 7.09 (pseudo-t, 2H,
para-H GePh2), 7.03 (pseudo-t, 2H, para-H CHPh), 3.19 (m, 8H,
NCH2), 1.64 (m, 8H, NCH2CH2), 1.38 (m, 8H, NCH2CH2CH2), 0.99
3
(t, 12H, JH–H = 7.3 Hz, NCH2CH2CH2CH3), 0.74 (s, 36H, CMe3). 13C
NMR (100 MHz, C6D6, 300 K): d 161.5 (CCHPh), 157.6 (CCHPh),
147.3 (ipso-C CHPh), 146.6 (ipso-C GePh2), 137.2 (ortho-C GePh2),
128.4 (ortho- and meta-C CHPh), 127.4 (meta-C GePh2), 127.1
(para-C GePh2), 126.6 (para-C CHPh), 59.3 (NC), 32.8 (CMe3), 24.5
(NCC), 20.6 (NCCC), 17.7 (CMe3), 13.9 (Me of n-Bu). IR (cmꢀ1, nujol,
CsI plates): 1829 vw, 1734 vw, 1699 w, 1657 vw, 1585 m, 1528 m
3. Experimental
m
(C@C), phenyl; 1458 vs, 1377 vs (nujol); 1306 m, 1261 w d (CH3);
1171 m, 1153 m, 1107 w, 1078 m, 1026 m, 1005 m, 928 s, 885 m,
860 s, 812 s, 737 s (CC), (CN), d (CC); 723 s (nujol); 700 m, 664 w,
623 m, 584 s, 523 m, 482 w, 465 m, 442 m (AlC), (GeC). Anal.
3.1. General
m
m
m
m
All procedures were carried out under an atmosphere of puri-
fied argon in dried solvents (n-hexane and cyclopentane with
LiAlH4; 1,2-difluorobenzene with molecular sieves; toluene with
Calc. for C60H94Al2ClGeN (991.4): C, 72.7; H, 9.6; N, 1.4. Found: C,
72.3; H, 9.5, N, 1.2%.
Na/benzophenone).
(Me3C)2Al-H
[17],
Me2AlH
[18],
3.3.2. [Ph2Ge{C(AltBu2)@CHPh}2Br][N(n–Bu)4] (3)
(H5C6)2Ge(C„C–C6H5)2 [7] and (H5C6)2Si(C„C–C6H5)2 [19] were
obtained according to literature procedures. Commercially avail-
able tetra(n-butyl)ammonium chloride and bromide were em-
ployed as purchased.
Yield: 83%. M.p. (sealed capillary, argon): 138 °C. 1H NMR
(400 MHz, C6D6, 300 K): d 7.63 (s, 2H, CHPh), 7.62 (pseudo-d, 4H,
ortho-H GePh2), 7.24 (pseudo-d, 4H, ortho-H CHPh), 7.14 (m, 4H,
meta-H GePh2), 7.12 (m, 4H, meta-H CHPh), 7.07 (m, 2H, para-H
GePh2), 7.02 (m, 2H, para-H CHPh), 3.23 (m, 8H, NCH2), 1.66 (m,
3
3.2. Synthesis of Ph2Ge[C(AltBu2)@CHPh]2 (1)
8H, NCH2CH2), 1.39 (m, 8H, NCH2CH2CH2), 1.00 (t, 12H, JH–
H = 7.4 Hz, NCH2CH2CH2CH3), 0.73 (s, 36H, CMe3). 13C NMR
(100 MHz, C6D6, 300 K): d 161.7 (CCHPh), 157.7 (CCHPh), 147.7
(ipso-C CHPh), 146.9 (ipso-C GePh2), 137.3 (ortho-C GePh2), 128.5
(ortho- and meta-C CHPh), 127.5 (meta-C GePh2), 127.1 (para-C
GePh2), 126.6 (para-C CHPh), 59.4 (NC), 32.9 (CMe3), 24.6 (NCC),
20.6 (NCCC), 17.9 (CMe3), 13.9 (Me of n-Bu). IR (cmꢀ1, nujol, CsI
A solution of di(phenyl)di(phenylethynyl)germane (0.160 g,
0.373 mmol) in 10 mL of n-hexane was added dropwise to a solu-
tion of di(tert-butyl)aluminum hydride (0.106 g, 0.746 mmol) in
10 mL of n-hexane at room temperature. The mixture was stirred
for 7 d and adopted a pale yellow color. All volatiles were removed
in vacuum. The solid residue was recrystallized from n-hexane (20/
ꢀ15 °C). Yield: 0.142 g (53%). M.p. (sealed capillary, argon): 188 °C
(dec.). 1H NMR (400 MHz, C6D6, 300 K): d 8.35 (s, 2H, CHPh), 7.89
(pseudo-d, 4H, ortho-H GePh2); 7.28 (pseudo-t, 4H, meta-H GePh2),
7.23 (m, 4H, ortho-H CHPh), 7.19 (m, 2H, para-H GePh2), 7.12 (pseu-
do-t, 4H, meta-H CHPh), 6.98 (pseudo-t, 2H, para-H CHPh), 0.92 (s,
36H, CMe3). 13C NMR (100 MHz, C6D6, 300 K): d 163.3 (CCHPh),
157.4 (CCHPh), 147.9 (ipso-C CHPh), 140.8 (ipso-C GePh2), 135.2
(ortho-C GePh2), 131.4 (meta-C CHPh), 129.6 (para-C GePh2),
129.2 (meta-C GePh2), 128.7 (para-C CHPh), 123.5 (ortho-C CHPh),
30.3 (CMe3), 19.4 (CMe3). IR (cmꢀ1, nujol, CsI plates): 1649 vw,
plates): 1655 m, 1599 m, 1574 m
vs (nujol); 1304 m, 1265 w d (CH3); 1169 s, 1153 s, 1082 m,
1068 m, 1028 m, 1001 w, 922 m, 889 w, 854 w, 812 m (CC),
(CN), d (CC); 723 vs (nujol); 703 sh, 629 w, 584 m, 521 m, 465
s, 436 w (AlC), (GeC). Anal. Calc. for C60H94Al2BrGeN (1035.9):
m(C@C), phenyl; 1466 vs, 1377
m
m
m
m
C, 69.6; H, 9.1; N, 1.4. Found: C, 69.9; H, 9.0, N, 1.4%.
3.4. Synthesis of MeAl[C(@CH–Ph)–SiPh2–C„C–Ph]2 (4)
A solution of dimethylaluminum hydride (0.045 g, 0.776 mmol)
in 10 mL of n-hexane was treated with a solution of diphenyl-
bis(phenylethinyl)silane (0.298 g, 0.776 mmol) in 10 mL of n-hex-
ane. The solution was heated under reflux for 4 h. All volatiles
were removed in vacuum at room temperature. The residue was
dissolved in a few mL of cyclopentane. Colorless crystals were ob-
tained on cooling to ꢀ15 °C. Yield: 0.224 g (71%). M.p. (sealed cap-
illary, argon): 75 °C (dec.). 1H NMR (400 MHz, C6D6, 300 K): d 8.14
1578 m
w d (CH3); 1155 m, 1088 w, 1026 w, 935 w, 918 m, 845 w, 808
w, 773 m (CC), d (CC); 723 s (nujol); 621 vw, 588 w, 548 w, 463
(AlC), (GeC). MS (EI, 20 eV, 100 °C, m/z; only the most inten-
m(C@C), phenyl; 1464 vs, 1377 vs (nujol); 1304 w, 1267
m
m
m
m
sive peaks are given, the complete isotopic patterns are in agree-
ment with the calculated ones): 657 (73%) [MꢀCMe3]+, 415
(100%)
[MꢀC(AltBu2)@CH–Phꢀbutene]+.
Anal.
Calc.
for
3
(s, 2H, JH–Si = 13.5 Hz, CHPh), 8.00 (m, 8H, ortho-H Ph2Si), 7.50
C44H58Al2Ge (713.5): C, 74.1; H, 8.2. Found: C, 73.2; H, 8.0%.
(pseudo-d, 4H, ortho-H alkynyl-Ph), 7.31 (pseudo-d, 4H, ortho-H
alkenyl-Ph), 7.25 (m, 8H, meta-H Ph2Si), 7.24 (m, 4H, para-H Ph2Si),
6.94 (m, 2H, para-H alkynyl-Ph), 6.92 (m, 4H, meta-H alkynyl-Ph),
6.85 (pseudo-t, 2H, para-H alkenyl-Ph), 6.65 (pseudo-t, 4H, meta-H
alkenyl-Ph), ꢀ0.92 (s, 3H, AlCH3). 13C NMR (100 MHz, C6D6,
300 K): d 160.9 (CHPh), 155.9 (C@CHPh), 145.6 (ipso-C alkenyl-
Ph), 136.4 (ortho-C Ph2Si), 135.6 (ipso-C Ph2Si), 132.6 (ortho-C alky-
nyl-Ph), 130.1 (meta-C alkenyl-Ph), 130.0 (para-C Ph2Si), 128.9
(para-C alkynyl-Ph), 128.6 (para-C alkenyl-Ph), 128.5 (meta-C alky-
nyl-Ph), 128.4 (meta-C Ph2Si), 125.7 (ortho-C alkenyl-Ph), 123.6
(ipso-C alkynyl-Ph), 110.3 (PhC„CSi), 91.9 (PhC„CSi), ꢀ7.2
3.3. Synthesis of [Ph2Ge{C(AltBu2)@CHPh}2X][N(n–Bu)4] (2 and 3);
general procedure
The tetra(n-butyl)ammonium halides (about 0.3 mmol) were
dissolved in 10 mL of toluene and slowly added at room tempera-
ture to a solution of an equimolar quantity of the diphenyl–
dialkenylgermanium compound 1 in 10 mL of the same solvent.
After about 10 min the products started to precipitate from the
clear solutions. Stirring was continued for 1.5 h. The suspensions

364
W. Uhl et al. / Inorganica Chimica Acta 374 (2011) 359–365
Table 1
Crystal data and structure refinement for compounds 1–5.a,b
1
2
3 1,2-F2C6H4
4 1,2-F2C6H4
5
Empirical formula
Temperature (K)
Crystal system
Space group [18]
a (pm)
C
44H58Al2Ge
C60H94Al2ClGeN
153(2)
C66H98Al2BrF2GeN
153(2)
C63H48AlF2Si2
153(2)
C36H39AlSi
153(2)
153(2)
orthorhombic
Pccn (no. 54)
1292.18(2)
1631.96(3)
1973.66(3)
90
90
90
4.1620(1)
4
1.139
monoclinic
P21 (no. 4)c
1208.91(2)
1986.45(2)
1239.31(1)
90
98.985(1)
90
2.93961(6)
2
triclinic
triclinic
monoclinic
Cc (no. 9)c
1683.15(2)
1641.22(2)
1128.80(1)
90
94.988(1)
90
3.10641(6)
4
ꢀ
ꢀ
P1 (no. 2)
P1 (no. 2)
1365.2(1)
2284.47(7)
2394.11(8)
115.778(1)
99.703(1)
94.500(1)
6.5297(7)
4
1206.16(5)
1260.78(6)
1903.96(9)
105.883(3)
96.349(3)
109.903(3)
2.5512(2)
2
b (pm)
c (pm)
a
(°)
b (°)
c
(°)
V (nm3)
Z
Dcalc (g cmꢀ3
)
1.120
1.170
1.206
1.126
1.088 (Cu Ka)
l
(mmꢀ1
)
1.598 (Cu K
a
)
1.667 (Cu K
a
)
1.150 (Mo K
a)
1.164 (Cu K
a)
Crystal size (mm)
0.45 ꢂ 0.42 ꢂ 0.21 0.41 ꢂ 0.32 ꢂ 0.28 0.16 ꢂ 0.13 ꢂ 0.05 0.16 ꢂ 0.08 ꢂ 0.05 0.15 ꢂ 0.13 ꢂ 0.07
U
range for data collection (°)
4.36 6 72.57
4037 (0.0297)
219
3.61 6 72.62
9145 (0.0470)
602
1.54 6 27.79
30 683 (0.0444)
1297
3.91 6 72.97
8632 (0.0376)
624
3.77 6 72.34
4951 (0.0245)
350
Independent reflections (Rint
Parameters
)
R1 [I > 2
wR2 (All data)
r
(I)]
0.0327 (3798)
0.0936
+0.606/ꢀ0.403
0.0699 (9005)
0.1788
+0.924/ꢀ0.775
0.0592 (19 817)
0.1693
+1.631/ꢀ0.877
0.0545 (5761)
0.1549
+0.452/ꢀ0.259
0.0330 (47 60)
0.0854
+0.253/ꢀ0.175
Maximum/minimum residual electron density (1030 emꢀ3
)
[w(Fo ꢀ Fc2))2]/
R .
[w(Fo2)2]}1/2
2
R1
=
R
||Fo| ꢀ |Fc||/
R
|Fo|; wR2 = {
R
a
Programme SHELXL-97 [20]; solutions by direct methods, full matrix refinement with all independent structure factors.
See Supplementary material for CCDC reference numbers.
b
c
Flack parameter: 0.00(2).
(CH3). 29Si NMR (79.5 MHz, C6D6, 300 K): d ꢀ28.4. IR (cmꢀ1, nujol,
1072 vs, 1043 vs, 1024 vs, 928 m, 885 m, 847 m, 797 m, 752 vs,
737 s (CC), d (CC); 721 s (nujol); 698 m d (phenyl); 627 m, 586
w, 523 s, 465 s, 420 w
CsI plates): 2156 m
m
(C„C); 2054 vw, 1954 w, 1892 w, 1825 vw,
m
1813 vw, 1771 vw, 1668 w, 1616 m, 1591 m, 1578 w, 1530 m,
1506 m (C@C), phenyl; 1456 vs, 1377 s (nujol); 1334 sh, 1302
m(AlC), m(SiC), d (CC). MS (EI, 20 eV, 100 °C,
m
m/z): 469 (17%) [MꢀBu]+, 385 (91%) [MꢀAltBu2]+, 308 (100%)
[PhSi(C@CH–Ph)(C„C–Ph)]+.
w, 1267 s d (CH3); 1206 m, 1179 m, 1155 m, 1105 s, 1076 m,
1024 m, 997 w, 966 w, 928 m, 893 s, 831 m, 800 m, 752 vs, 737
vs
m(CC), d (CC); 700 s d (phenyl); 631 m, 615 w, 590 m, 565 m,
3.6. Crystal structure determinations
534 s, 494 s, 478 s, 467 s, 438 m, 411 s, 363 m, 334 w
m(AlC),
m
(SiC),
d
(CC). MS (EI, 20 eV, 90 °C, m/z): 384 (100%)
Single crystals were obtained by crystallization from n-hexane
(20/ꢀ15 °C, 1), 1,2-difluorobenzene (20/ꢀ15 °C, 2 and 5) and cyclo-
pentane with a small quantity of 1,2-difluorobenzene (20/+2 °C,
3ꢁ1,2-C6F2H4; 20/ꢀ15 °C, 4ꢁ1,2-C6F2H4). The crystallographic data
were collected with a Bruker APEX diffractometer. The crystals
were coated with a perfluoropolyether, picked up with a glass fiber
and immediately mounted in the cooled nitrogen stream of the dif-
fractometer. The crystallographic data and details of the final R val-
ues are provided in Table 1. All non-hydrogen atoms were refined
with anisotropic displacement parameters; hydrogen atoms were
calculated on ideal positions and allowed to ride on the bonded
atom with U = 1.2Ueq(C). The molecules of compound 1 reside on
a crystallographic twofold rotation axis with the germanium atom
on a special position. Compound 3 has two independent molecules
in the asymmetric unit. One of the 1,2-difluorobenzene molecules
and a butyl group are disordered; their atoms were refined on split
positions. The crystals of 4 enclose one molecule of 1,2-difluoro-
benzene per formula unit. A fluorine atom is disordered and occu-
pies two positions. Only three hydrogen atoms were considered in
this case.
[Ph2Si(C@CH–Ph)(C„C–Ph)ꢀH]+,
307
(42%)
[PhSi(C@CH–
Ph)(C„C–Ph)ꢀH]+.
3.5. Synthesis of tBu2Al–C[@C(H)–Ph]–SiPh2–C„C–Ph (5)
A solution of compound 4 (0.278 g, 0.342 mmol) in 25 mL of tol-
uene was treated with a solution of di(tert-butyl)aluminum hy-
dride (0.097 g, 0.685 mmol) in 10 mL of toluene at room
temperature. The solution was stirred for 4 h. All volatiles were re-
moved in vacuum. The residue was dissolved in 1,2-difluoroben-
zene. Pale yellow crystals of 5 were obtained upon cooling of the
solution to ꢀ15 °C. Yield: 0.254 g (71%). M.p. (sealed capillary, ar-
gon): 109 °C (dec.). 1H NMR (400 MHz, C6D6, 300 K): d 8.17 (s,
1H, 3JH–Si = 13.7 Hz, CHPh), 8.00 (m, 4H, ortho-H Ph2Si), 7.51 (pseu-
do-d, 2H, ortho-H alkynyl-Ph), 7.27 (m, 4H, meta-H Ph2Si), 7.22 (m,
2H, para-H Ph2Si), 7.14 (pseudo-d, 2H, ortho-H alkenyl-Ph), 7.07
(pseudo-t, 2H, meta-H alkenyl-Ph), 6.97 (pseudo-t, 1H, para-H
alkenyl-Ph), 6.92 (m, 2H, meta-H alkynyl-Ph), 6.91 (m, 1H, para-H
alkynyl-Ph), 1.12 (s, 18H, CMe3). 13C NMR (100 MHz, C6D6,
300 K): d 158.8 (CHPh), 157.1 (C@CHPh), 146.8 (ipso-C alkenyl-
Ph), 135.9 (ortho-C Ph2Si), 135.0 (ipso-C Ph2Si), 132.8 (ortho-C alky-
nyl-Ph), 130.8 (meta-C alkenyl-Ph), 130.1 (para-C Ph2Si), 129.6
(para-C alkynyl-Ph), 129.0 (para-C alkenyl-Ph), 128.6 (meta-C alky-
nyl-Ph), 128.5 (meta-C Ph2Si), 124.3 (ortho-C alkenyl-Ph), 122.7
(ipso-C alkynyl-Ph), 111.8 (PhC„CSi), 92.1 (PhC„CSi), 30.5
(CMe3), 19.4 (CMe3). 29Si NMR (79.5 MHz, C6D6, 300 K): d ꢀ34.5.
Acknowledgments
We are grateful to the Deutsche Forschungsgemeinschaft for
generous financial support.
Appendix A. Supplementary material
IR (cmꢀ1, nujol, CsI plates): 2156 m
1965 w, 1948 vw, 1890 vw, 1817 vw, 1769 vw, 1694 vw, 1653
vw, 1597 m, 1539 vw, 1506 m (C@C), phenyl; 1460 vs, 1377 s (nu-
jol); 1304 m, 1269 m d (CH3); 1217 w, 1169 m, 1155 m, 1101 vs,
m(C„C); 2122 m, 2033 vw,
CCDC 808916–808920 contain the supplementary crystallo-
graphic data for 1–5. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
m

W. Uhl et al. / Inorganica Chimica Acta 374 (2011) 359–365
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